.uasset files that were deleted then re-added to the Content Browser are not properly discovered and added to the explorer. I have confirmed these assets are still on disk within Windows Explorer. The only workaround I've found is to restart the editor or reloading the project.
This occurs in //UE4/Release-4.24 cl 11590231 so I am not marking this as a regression.
None of the .uasset files are discovered, the feature pack folders are empty
Added feature pack content is discoverable
Reload the project and the assets will be visible in the content browser
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-96701 in the post.